1. Field of the Invention
The present invention relates to an equalizer of a digital optical disk recording/reproducing system, and more particularly, to a fixed delay tree search/decision feedback equalizer using an absolute value calculation in a reproducing terminal which reproduces a data passing through a channel and a data restoring method using the same.
2. Description of the Background Art
Recently, as a recording density of a recording medium of an optical recording/reproducing system increases, an intersymbol interference is increased between recording data. Thus, a technique allowing a reading terminal of the recording/reproducing system to accurately restore a data is required.
FIG. 1 is a schematic block diagram showing the construction of a general digital optical recording/reproducing system.
As shown in FIG. 1, a data recording terminal 100 of the digital optical recording/reproducing system includes an A/D converter 110 sampling an image/audio signal to digital data; a coding unit 120 for coding the image/audio signal; a recording waveform generating unit 130 generating a recording waveform according to a characteristic of an optical recording medium; a laser disc (LD) drive unit 140 driving an optical diode corresponding to the recording waveform, and a phase lock loop (PLL) 150 for synchronizing in recording a data.
A data reading terminal 200 of the digital optical recording/reproducing system includes: a radio frequency amplifying unit 210 reading and amplifying a data stored in the optical recording medium; an automatic gain controller 220 controlling a gain of the radio frequency amplified signal; a synchronizing unit 240 compensating a time delay; an A/D converter 230 sampling the gain controlled signal to digital data; an equalizer 250 restoring the sampled digital data; a decoding unit 260 removing a noise generated to the restored digital data and detecting and correcting an error for channel transmission; and a D/A converter 270 restoring the decoded digital data to its original image/audio signal.
The operation of the digital optical recording/reproducing system constructed as described above will now be explained.
First, the A/D converter 110 samples an inputted image/audio signal and converts the signal into a digital data.
Then, the coding unit 120 codes the digital data in order to minimize an error or a noise in transmission of the digital data through channel.
Then, the recording waveform generating unit 130 generates a waveform for being recorded in a storing medium according to the coded digital signal, and the LD drive unit 140 records a signal corresponding to the waveform in the storing medium 160.
The radio frequency amplifying unit 210 amplifies the signal detected from the storing medium 160, and the automatic gain controller 220 controls the gain of the amplified signal to a certain level.
Then, the A/D converter 230 samples the gain-controlled signal to digital data, and the equalizer 250 restores the sampled signal as a data.
At this time, the synchronizing unit 240 synchronizes the equalizer 250 and the A/D converter 230 in order to prevent occurrence of a time delay in sampling and data restoring.
Thereafter, the decoding unit 260 removes a noise of the data generated in transmitting it through a channel, detects and corrects an error, and then, the D/A converter 270 restores an original image/audio signal.
At this time, in order to restore an accurate data, the equalizer 250 of the reproducing terminal 200 generally uses a decoding algorithm of a maximum likelihood sequence detection (MLSD) method.
However, the MLSD method is implemented on the basis of a means square error (MSE) in which a minimum distance is computed by the square of an error between the signal inputted to the equalizer 250 and a reference signal and a decoding is performed according to a path metric that accumulates the computed minimum distances.
However, a multiplier used for the minimum distance computation exposes the following problems.
That is, in a high density digital video disc (DVD) system of 15 GB (giga byte) level, a calculation speed of a higher speed is requested, and if it is substantially implemented as an application-specific integrated circuit (ASIC), the computation amount is increased, so that a calculation speed is slow. And since many gates are used, a chip is enlarged in size.
In addition, in order to improve the speed in operating the minimum distance using the MLSD method, if a different calculation method (i.e., an absolute value calculation) is used, a performance is rather degraded.